Electrical apparatus for detecting the presence of moving objects



April 8, 1952 J. COLLARD ELECTRICAL APPARATUS FOR DETECTING THE PRESENCEOF' MOVING OBJECTS Filed April 3, 1946 1N V EN TOR.

Patented pr. 8, 1952 ELECTRICAL APPARATUS FOR- DETECTING. THEPRESENCELOF MOVING .OBJ ECTS i JohnCollard, London, England, assg'nor toElec-` tric and Musical Industries, Limited, a British ApplicationApril, 1946, Serial No. 659,196 In Great Brit-ain January 20,1941

Section 1,1 Public Law 690, August'v8f1946 Patent expires J anuaryl 2U,1961 (Cl. A343,49 )f 16 claims. l

This inventionrelates to electricalmethods and apparatus fon detectingthe presence of moving objects.

It has been proposed to detect the presence of movingobjects such aslaircraft byA transmitting at spaced time intervals high frequencyoscilla-V tions-inthe Vform of-pulses of short duration, the signalsbeing transmitted from some form of directive'aerial and the signalsreile'cted bythe aircraft and received by a suitable receiver serving toindicate, by measuring the time interval betweenthe transmission of apulse and thereception-ofits reiection, the distance away of the movingobject. It is also possible torobtain an indication-of thewposition ofthe moving object with respect to the point of transmission orrecaption.

In the case'where it is desired to-ascertain the distance of the objectfrom the transmitter, the time interval between the transmissionand/reception ofv a pulse is usually measured by means of la cathode-ray tube the beam of which is caused to-travel horizontally acrossthescreen oth'e tube ata vpredetermined rate; Atthe instant-of'transmittinga signal a verticaldefiection Vis imparted to the beam which thusproduces avertical trace on the screen whichconstitutes the 'zeroonthehorizontal scale. When -a reilected'signalis received it is'ampliiedandappliedto the cathoderay tube producing a second reected 'signalsarereceivednot only fromlthe moving object which is to be located, but.also from stationary objects on the ground, Asuch'as buildingsY andhills. The vertical traces produced onthe screen o'f the cathode raytube by these unwanted reflections from stationaryl objects maypartially or-entirely obscure thetrace produced by the signal receivedfrom the moving object and since it is not readily possible tovdistinguish'the Wanted from the unwanted traces accurate location ofthe vmoving Aobject is' not possible..

The object of thepresentinvention istofprovide an improved method of andapparatus for facilitating distinction between'signals received frommoving objectsv and si'gnalsreceived from stationary objects.

The invention is based on the fact that the phase ofthe oscillations ofthe reflected signals changes with respect to the phase of theioscilla.-tions of :the transmitted signals as the object 2;' moves,.whilstt inthecase4 oi' signals; reected from stationary objects thephaseiof. theoscillations of '.the` signals received yfromisucll objects lrernainsxed with `respect to: thephase of the oscillations of thesignalstransmitted.Z ItisjpossiloleA to convert these,phasevariationslintoamplitude variations sovithat successive signals received froml'amovingv .object will lvary inlamplitude `While suc:- cessive signalsreceived from'. stationary `objects will remain of constant:amplitude.A

Thus,` according?. ton the present. invention there is. provided .aVmethod ,of detecting: the l presence'. of i a Anfiovingsolojectwhichrcomprises transmitting. oscillatory 'signals rat. spaced rtimevintervalsand receiving said signals after. reflection by said. object,:whereinlinr order .to distinguish signals reflected by said. movingobject. from `signalsareected .byfstationary1 objects theI change orAphasev which. occursfbetweenJthc signals .re-

ceived from' said moving object'and .signalsbea'ring a fixed phaserelationship .with nthe .signals transmitted, .as saidr object moves'.is; `utiliz/.ed l to enable successive'signalsreceived from said movingobject to be converted into; signalslof: varying amplitude. Thus, bycomparing the reflected signals received after the transmission of oneburst of oscillation with'the signals received from the previousburstfofoscillation, it is vpossiblefto distinguishthe. signals received from amoving .object since.- the amplitude of the signal. ycorresponding tovthe1 first-mentioned bursty off oscillation Willbe changed compared,Withthe' amplitude of the signal corresponding-to saidprevious burst ofoscillation.

The invention provides apparatus for converting the change of phase intoa variation in amplitude, and for eiectively ,separating signalsreceived from stationary objectsfrom' signals re.- ceived from a movingobject sothatlthetraceon the cathode ray tube will'not be obscuredby thepresence. of reections from stationary objects.

Inv order that. theinvention may bemore clearly'junderstood Aandreadilydcarried into effect a method andapparatus-fordetectin'g the presence or`the vdistance of a movin'gobjectWill'nowbe described in ,greatervdetail by way ot example with .referenceto the l drawing in which:

Figure 1 is an explanatory. diagram ofthefinvvention, and

Figure 2 illustrates lfdiagrammaticallyal form of -electricallyoperated-switch for use inseparatingl signals received vfrom Astationaryobjects from signals received from` moving objectsfV f In-the twofigures, similar parts are `indicated by similar reference characters.

The invention will be described with reference to Figs. l and 2 asapplied by way of example to a method and apparatus for detecting thepresence of aircraft. In such case a suitable form of transmitter I isprovided which generates a carrier wave of a frequency of, for example,100 megacycles per second, this carrier wave being modulated by shortpulses of, for example, `2 microseconds duration occurring every 1300microseconds. The transmitter may comprise a radio frequency oscillator2, a power amplier 3, a pulse generator 4, and a modulator 6 for pulsemodulating the ampliiied carrier wave. These signals are transmittedfrom a suitable directive aerial lIrand after reflection are received,amplied and fed to a cathode ray tube 8V upon theV luminescent screen ofwhich vertical traces are caused to appear with the transmission of asignal and with the reception of a reflected signal so as to afford ameasure of the distance of the aircraft. The change of phase whichoccurs with signals received from a moving object is utilized incarrying out the present invention by converting successive signals ofdifferent phase received from moving objects into signals of varyingarnplitude so as to permit ready comparison to be made between signalsreceived from stationary objects, the amplitudes of which will remainconstant during successive cycles.

The conversion of the change of phase into an amplitude variation can beeiected in a variety of ways by mixing with the oscillations of thereceived signals, some of the original carrier oscillations aftersuitably adjusting the amplitude o-f the latter and the mixed signalsmay be passed through a rectier which produces in its output circuit asignal the amplitude of which is dependent upon thephase differencebetween the mixed oscillations. If a carrier wave E sin wt istransmitted and a stationary object at a distance d reflects some of thetransmitted energy back to a receiver the reflected wave on receptionwill be delayed by a time where 'u is the velocity of thev wave. Bymixing the oscillations of the reflected signals with the carrieroscillations and passing them through a rectier a term of the form E sinwt sin (wt-HJ) will be produced where is the angle correspond- 'ing tothe delair The average value of this term taken over a succession oftransmitted pulses is proportional to cos 0 and is therefore dependenton the distance d.

Thus, if the object is stationary so that d is constant, cos 0 wouldalso be constant, but if the object is moving relatively to thetransmitter, d will vary and likewise cos 0 will vary. Hence, therectied'signals derived from signals received from a stationary objectwill be of constant amplitude whilst the amplitude of the rectifiedsignals derived from a moving object will vary. It will, therefore, beappreciated that by comparing successive signals received over apredetermined period it is readily possible to determine the signalsreceived from moving objects since, of course, the amplitude of suchsignals will vary, whereas the amplitude of signals received fromstationary objects will remain constant over said period.

It is preferred in utilizing the invention where the received signalsare applied to a cathode ray tube to eiect the necessary separation ofthe signals received from the moving object from the Signals receivedfrom stationary objects by a suitable form of switching device whichenables the signals received after transmitting a signal to be comparedwith the signals received after transmitting the previous signal. Asshown in Fig. 1, the reference numeral I3 indicates a re-l ceiver whichproduces output signals the amplitudes of which are dependent on thephase difference between the oscillations of the signals transmitted andthe oscillations of the signals received. The receiver may contain amixing circuit of the form used in a superheterodyne receiver, signalsfrom the transmitter and received signals being together applied to themixer which should have a square law to give the term E sin wt sin(wt-i-v) previously referred to.

The output of the receiver is arranged to be fed in succession over apredetermined time interval to a series of condensers I4, one of theelectrodes of each condenser being connected together and to a commonresistance I5, one end of which is earthed, as shown. The junction ofthe resistance and the condensers is connected to an amplier I6 whichamples signals appearing across the resistance I5 and applies them to acathode ray tube 8, the beam of which is caused to travel across thescreen of the cathode ray tube at a predetermined rate by means of adeiiecting circuit 9 so that any signals appearing across the resistanceI5 will cause a vertical deflection of the beam. As the beam commencesto travel across the screen, .a switch arm I8 commences to traverse theseries of condenser contacts, thus connecting the output of the receiverto the condensers in turn so that the output of the receiver during theperiod that the beam is travelling across the screen is appliedsuccessively to the series of condensers. When the beam reaches itslimit of travel, it is returned to the initial position to commence afurther cycle and the contact arm I8 is likewise returned to the rstcondenser contact so as to recommence its cycle. As the switch arm I8and the beam commence their travel, a signal is transmitted by thetransmitter and if at' any instant thereafter, a reflected signal isreceived the output of the receiver I3 will be applied to whichevercondenser the switch arm is in contact Awith at that instant so that achargewill accumulate at the condenser depending on the amplitude of thesignal appearing at that instant in the output of the receiver.

Thus, throughout the cycle if a reilected signal is received either froma stationary or a moving object some of the condensers will be chargedto an appropriate value. As the switch arm commences a further cycle afurther signal is transmitted and further reected pulses are received.If a reflected pulse is received from a stationary object the voltageproduced in the output of the `receiver at that instant will be the sameas it was in the previous cycle at the corresponding instant and henceno additional charge will be applied to the appropriate condenser sothat no curwill have been f produced during the interval =,be-

tween successive` signals, the voltage-appearing inV the output ofthereceiver` I3 will'notf berthe same as 'itwas at the correspondinginstant in the previous cycle so that current will fiowinto or iout ofthe appropriate condenser to-charge -it to a newevoltageysuch currentflow through the resistance I5 ycausing a vertical deection of the beamof vthecathode ray tube'. Thus, asthe switch` arm I8'successivelyVconnects the condensers lto the outputof the receiver `I3 no verticaldeflection is applied to4 the -catho'de ray beam so long vas novariation =in-the-charge-of the condensers occurs comparedwith'thecharge l ofthe previous cycle. When, howeverya-signal. from amoving object is received the condenser tok which the switch. ann isthen connected changes' its charge and a vertical-deflection-is impartedto the beam of the cathode raytube.

It will thin be appreciated that 'afterafew cycles a steady state isestablished and the only vertical deiiection of the beam that -oc'cursafter the transmission of a signal in one cyclewillbe that due to thereceipt of the signal from a moving object. Hence, vany tendency forsuch de' ection to be obscured bydeections due to signals received forstationaryobiects will be removed.

It is', ,of course, impracticable to use a mechanical switch such as isdiagrammatically shown in Figure 1 and, accordingly, a preferred formOfswitch is one in which'theswitching operation is effectively performedelectronically. Suche. form of switch is shown in Figure 2 and compriseswithin an evacuated envelope a cathode ray gun I9, diagrammaticallyindicated, which generates a beam of electrons which is deflectedinvsucha manner thatitimpinges in turn onta series` of conductingelementslil, mounted 0n an insulating plate I, such as a sheet of mica,which is backedby a conducting plate 22. The conduct,- ingkelements 2uare composed of material which readily emits, Vsecondary v electronsunder bombardmentby a beam of primary electrons and in association withther insulating plate 2l and the conductingplate 22 they form a seriesof condensers..

Preferably, the conducting elements 20 are a1'- ranged in the-form f acircle and the cathode ray beam from the gun I9 is caused to impingeonthe elements 20Y by deecting the, beam by means of a deflectingcircuit 25 under the actionv of a suitable rotating eld. Disposed infront oi the elements 20 is a grid 23 towhich the output of the receiverI3 is; connected. The conducting plate 22 is connected toV a resistance`I5 earthed as shown and the junction between ,the conducting plate22and the resistance I5 'is connected to the amplier I6. l

As the beam from the cathode ray gun impingeson the elements 20 in turneach element is caused to emit secondary electrons and due to thepotentiall ofthe grid 23 which is connected asstated above to the outputofthe receiver I3 these secondary -electrons will be repelled oratv.tracted, so causing the individual vcondensers to charge ordischarge and producing a voltage difference across the resistance I5 ifthe charge across the condenser differs from what it was in the previouscycle. Thus, the arrangement operates in a manner similar to themechanical switch described in Figure 1.

The presence of a moving object may, as pre'- vviously "stated, beindicated by vertical deflecf tions of a horizontal trace ontheiiuorescentV screen*-r of` a ,1 cathode ray .tube corresponding Y tothe tubeea in-Figure .1.= In order toprovide an indication of thedistance ofthe movingobject, an `initialrvertical deection is impartedto .the electron beam of the tube 8 simultaneously with thetransmissionof the signal-.or burst .of oscil- 1ations,1the A.reflection fof which.provides the indication;I The fluorescent screen is` provided with a:graduated scale suitably proportioned with :the

ratecf traverse of the beam across the screen of theftube.-

Itis possiblerthat due to the capacity Ybetween thegrid 23 and theconducting plate 22` any voltageapplied Vto the .grid 23 bythe receiverwill cause-:current to ow .through this capacityand so produce'undesireddeflectionsV of the cathode ray ,beam inthe tube. To overcome this'defect thevcapacity'-between-an-element 20 Yand the plate l22 vmust bevmade large lcompared .with the capacity between thegrid `2,3 and theplate 22 or, alternatively, or in addition, the undesired effect may beneutralized by feeding from the receiver I3 tothe plate 22 through asuitable condenser a voltage 180; out of phase with the voltage appliedto the Igrid 23.

Although the invention is of special applicatlonior detectingzthe4presence of aircraft, it will be appreciated thatvitcan be-appliedfondetecting the presence of other moving objects. Again. although thepresence or distanceof an object is, Vin the particular exampledescribed, indicated visually, it will'be understood that the method ormeans providing vthe vindication are immaterialfto the invention and,for example, an audible indication maybe provided.

I claim as my invention:

1. Apparatus for detecting the .presence of a moving object comprisingmeans for transmitting oscillatory signals in bursts at spaced timeintervals and means for receiving said signals after reflection by saidobject and wherein, in order to distinguish signals reilected by saidmoving ob ject from signals reflected by stationary objects, means areprovided to convert into amplitude changes the phase changes which occurbetween successive signals reflected from said moving yobject by virtueof its movement and oscillations bearing a fixed phase relationship withthe signals transmitted, saidvlast-mentioned means including means forcomparing the signals received after one burst of oscillation with thesignals received after a second burst of oscillation'and further vmeansfor separating signals' of -substantially the same amplitude -fromthosesignals whose amplitude has changed, said separated signalsfbeingapplied to'an indicating device, sai-d meansfor comparing and -forseparating-signals including individual storage devices and vmeans forapplying the signalsreceived after one burst oi oscillation to saidstorage devices, said last means serving to apply corresponding receivedsignals after the next Iburst of oscillationto the same storagedevices,-said storage devices being arranged to provide an output if thesignals applied tosaid-storage devices change in amplitude.

2.' Apparatus forV detecting'the presence of 'a moving object comprisingmeans for transmitting oscillatory signalsin burstsl at spaced ltimeintervals and means for receiving lsaid signals after reection fby saidobject and wherein, in order to distinguish signals reflected bysaidmoving object from signals reflected by ystationary objects, meansare provided to 4convert into amplitude changes the phase changes whichjoccur between successive signalsireected from said movingobj'ect byvirtue of its movement and oscillations bearing a fixed phaserelationship with the signals transmitted, said last-mentioned meansincluding means for comparing the signals received after one burst ofoscillation with the signals received after a second burst ofoscillation and further means for separating signals of substantiallythe same amplitude from those signals Whose amplitude has changed, saidseparated signals being applied to an indicating device, said means forcomparing and for separating signals including a cathode ray tube havinga signal plate which has storage elements associated therewith to form aseries of condensers and means comprising a control electrode in thevicinity of said elements to which signals from said amplitudeconverting means are supplied for applying the signals received afterone burst of oscillation to said storage elements, said last meansserving to apply corresponding received signals after the next burst ofoscillation to the same storage elements, and means for causing theelectron beam of the cathode ray tube to traverse said elementssuccessively whereby an output may be taken ci said signal plate if thesignals applied to said elements change in amplitude.

3. Apparatus according to claim l, wherein said indication is visual andis provided by a cathode ray tube and including means for causing theelectron beam of the tube to trace a pattern, such as a line, which ismodified on reception of a succession of signals from a moving object toindicate thepresence or the distance of said object.

4. Apparatus according to claim 2, wherein the indication of thepresence or distance of a moving object is visual and means are providedfor causing the electron beam of a cathode ray tube providing saidvisual indication to commence the traverse of a pattern simultaneouslywith the transmission of a signal and further means are provided tocause the electron beam of the cathode ray tube containing said storageelements simultaneously to commence its traverse of said elements.

5. Apparatus according to claim 2, wherein in order to reducedeleterious effects due to capacity between said control electrode andsaid signal plate, the capacity between the individual elementscooperating with the signal plate, and said signal plate is made largecompared with the capacity between said control electrode and saidsignal plate. A

6. In combination, means for comparing the phase of one signal with thatof another signal and for supplying an output signal of varyingamplitude in response to variations in the phase relation oi' saidsignals, means comprising a cathode ray storage tube for passing saidvarying ,amplitude signals to the exclusion of constant amplitudesignals, said storage tube providing internal cancellation of constantamplitude signals, an indicator, and means for supplyingv to saidindicator the varying amplitude signals passed by said storage tube.

'7. In combination, means for transmitting oscillatory signals, meansfor receiving said signals after reiiection from an object, saidreceiving means including means for mixing said received signals withsignals whose oscillations provide a phase reference whereby there areobtained signals which are of varying amplitude when reiiected frommoving objects, means comprising a cathode ray storage tube for passingsaid varying amplitude signals to the exclusion of constant amplitudesignals, and means "for taking said varying amplitude signals off saidstorage tube.

8. In combination, means for transmitting pulses of oscillatory signals,means for receiving said signals after reflection from an object, saidreceiving means including means for mixing said received signals withsignals whose oscillations bear a Xed phase relationship with theoscillations of the signal pulses transmitted whereby there are`obtained signals which are of constant amplitude when reflected fromxed objects and signals of varying amplitude When reflected from movingobjects, means comprising a cathode ray storage tube for passing saidvarying amplitude signals to the exclusion lof said constant amplitudesignals, an indicator, and meansv for supply;- ing said varyingamplitude signals to said indicator.

9. Apparatus for detecting thepresence of a moving object comprisingmeans for transmitting oscillatory signals in bursts at'spaced timeintervals and means for receiving said signals after reflection by saidobject and wherein, in order to distinguish signals reflected from saidmoving objects from signals reflected by stationary objects, means areprovided to convert into amplitude changes the phase changes which occurbetween successive bursts of signals reflected from said moving objectby virtue of its movement and oscillations 4bearing a fixed phaserelationship With the signals transmitted, means comprising a cathoderay storage tube for separating the pulses of varying amplitude fromthose of constant amplitude, a cathode ray indicator tube, and meansforsupplying said varying amplitude pulses from said storage tube tosaid indicator` tube. 10. In combination, a pulseV transmitter, a, re-

' oeiver to receive reflected signals, means for constorage period by asecond transmitted pulse whereby said storage period is equal to and isa function of the time interval between said first and secondtransmitted pulses, means for storing a received signal for the durationof said storage period, and means for comparing with said stored signalsreceived at a latenetime interval that is equal to the period betweensaid first transmitted pulse and said second transmitted pulse.

ll. Apparatus for detecting the presence of a moving object comprisingmeans for transmitting oscillatory signals in bursts at spaced timeintervals and means for receiving said signals after reiiection by saidobject and wherein, in order to distinguish signals reilected by saidmoving object from signals reflected by stationary objects, means areprovided to convert into amplitude changes the phase changes which occurbetween successive signals reflected from said moving object by virtueofits movement and oscillations bearing a xed phase relationship withthe signals transmitted, and further means being provided for utilizingsaid amplitude changes to provide an indication of the presence of saidmoving object, said last means comprising means to compare the signalsreceived after one burst of oscillation with the signals received aftera second burst of oscillation, further means being provided forseparating signals of substantially the same amplitude from thosesignals Whose amplitude has changed, an indicating device, and means forapplying said separated signalsto said indicating device.

comprising a cathode ray storage tube for passing said varying amplitudesignals to the exclusion of constant amplitude signals, said cathode raystorage tube being of the single electron gun type comprising a storagescreen having capacity storage elements, means for sweeping the cathoderay repeatedly across said storage screen in synchronism with said pulsetransmission whereby the storage elements of said storage screen acquirean equilibrium potential due to secondary electron emission so long asno signals of changing amplitude are applied to said storage tube, meansfor applying the output signals of said receiving means to said storagetube to upset said equilibrium potential in response to any change inthe amplitude of said output signals,

and means for taking oi said storage tube the signals resulting fromsaid upsetting of said equilibrium potential.

13. In combination, means for transmitting pulses of oscillatory radiosignals toward a reilecting object, means for receiving said signalsafter reflection, said receiving means including means for mixing saidreceived signals with phase comparison signals whereby output pulses ofvarying amplitude are produced in response to variations in the phaserelation of said signals, a cathode ray storage tube of the singleelectron gun type comprising a storage screen having capacity storageelements and a screen electrode immediately adjacent to said storagescreen and on the gun side thereof, means for sweeping the cathode rayrepeatedly across said storage screen in synchronism with thetransmission of said pulses whereby the storage elements of said storagescreen acquire an equilibrium potential due to secondary electronemission so long as no signals of changing amplitude are appli-ed tosaid storage tube, means for applying the output signals of saidreceiving means to said storage tube to upset said equilibrium potentialin response to any change in the amplitude of said output signals, andmeans for taking off said storage tube the signals resulting from saidupsetting of said equilibrium potential.

14. In combination, means for transmitting oscillatory signals, meansfor receiving said signals after reection from an object, said receivingmeans including means for mixing saidreceived signals with signals whoseoscillations bear a fixed phase relationship with the signalstransmitted whereby there are obtained signals which a-re of constantamplitude when reflected from xed objects and signals of varyingamplitude when reflected from moving objects, means comprising a cathoderay storage tube for passing said varying amplitude signals to theexclusion of said constant amplitude signals, said storage tubeincluding a storage screen comprising a sheet of insulating materialhaving a conducting sheet or back plate on one side and having capacitystorage elements on the opposite or front side, a screen electrodepositioned in front of and immediately adjacent to said storageelements, means for producing an electron beam and directing it throughsaid screen and against said capacity storage elements whereby they emitsecondary electrons to bring said storage elements to an equilibriumpotential, means for causing said electron beam to sweep across saidstorage screen successively whereby signals are passed by said tube onlyin response to a `change in said equilibrium potential caused by theoccurrence of said varying amplitude signals.

15. In combination, means for transmitting pulses of oscillatory radiosignals toward a refleeting object, means for receiving said signalsafter reection, said receiving means including means for mixing saidreceived signals with signals whose oscillations have a xed phaserelationship with the oscillations of the transmitted signals, a cathoderay storage tube of the single electron gun type comprising a storagescreen having capacity storage elements on the electron gun side thereofand having a conducting surface en the other side thereof, a screenelectrode immediately adjacent to said storage screen and on the gunside thereof, means for sweeping the cathode ray repeatedly across saidstorage screen in synchronism ywith the transmission of said pulseswhereby the storage elements of said storage screen acquire anequilibrium potential due to secondary electron emission so long as nosignais of changing amplitude are applied to said storage tube, meansfor varying the potential difference between said screen electrode andsaid conducting surface by the output signals of said receiving means toupset said equilibrium potential in response to any change in theamplitude of said output signals, and means for taking ofi said storagetube the signals resulting from said upsetting of said equilibriumpotential.

16. Apparatus for detecting the presence of a moving object comprisingmeans for transmitting oscillatory signals in bursts at spaced timeintervals and means for receiving said signals after reection by saidobject and wherein, in order to distinguish signals reected from saidmoving object from signals reflected by stationary objects, means areprovided to convert into amplitude changes the phase changes which occurbetween successive bursts of signals reected `from said moving object byvirtue of its movement and oscillations bearing a xed phase relationshipwith the signals transmitted, means for separating the resulting pulsesof varying ampliture from those of constant amplitude, said last meanscomprising a cathode ray storage tube having a storage screen and havingmeans for producing an electron beam and directing it against saidstorage screen, means for sweeping said electron beam across said screenin a predetermined time relation with respect to the transmission ofsaid bursts of signals, a screen electrode positioned adjacent to saidstorage screen and on the beam side thereof, and means for applying saidresulting pulses to said screen electrode.

JOHN COLLARE'.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,750,668 Green Mar. 18, 19302,189,549 Hershberger Feb. 6, 1940 2,193,361 Rice Mar. 12, 19402,403,625 Woli July 9, 1946 2,412,631 Rice Dec. 17, 1946

